Many types of heavy rotary machinery, including pumps, compressors, and turbines, (hereinafter a “rotary machine”) produce work by means of a working fluid enclosed within a working chamber as its main shaft is rotated. Although the clearance between the shaft and the rotary machine housing is relatively small, the working fluid tends to leak from each housing opening through which the shaft extends (hereinafter referred to as a “shaft opening” for brevity). A seal is generally used in the proximity of a shaft opening, to prevent the leakage of working fluid therefrom.
Numerous seal types are known. For low speed rotary machines, a known seal type is a spring loaded gasket, such as an O-ring. For high speed rotary machines, one common type is the mechanical seal which consists of radial planar surfaces normal to the shaft axis and machined to surfaces of low surface roughness. One surface is gasketed to the housing while a second surface is driven by the shaft and sealed thereon by a secondary seal such as a bellows. Such a seal is generally expensive and tends to rupture at once without any prior indication. The repair of a faulty mechanical seal is costly and time consuming, necessitating extensive rotary machine downtime. Another type of high speed rotary machine seal is the compression rope packing seal. This type of seal abrades the shaft surface during a tightening and adjustment procedure. Although the rope packing slowly loosens and therefore provides early indication as to working fluid leakage, the packing material erodes relatively quickly due to frictional heat buildup and needs to be replaced often by the time consuming replacement procedure. Another known seal type is the labyrinth seal, which employs stationary teeth disposed in such a way that there is a small clearance between the teeth and the shaft periphery, in order to restrict flow by means of a torturous path and induced turbulence. Labyrinth seals are suitable for high shaft speeds; however they require accurate positioning with respect to the shaft and are therefore relatively expensive.
The present invention relates to the type of sealing material that is a high-viscosity non-Newtonian liquid, i.e. its viscosity varies as a function of its shear stress, and is made of a blend of synthetic fibers, lubricants, and binding agents (hereinafter referred to as the “sealant”). Such a sealant is generally introduced under pressure by an injection device, such as a manually operated injection gun, into a stuffing box which surrounds the shaft from an inlet port on the stuffing box exterior. Following injection of the sealant into the stuffing box, the inlet port is occluded with a suitable plug. The applied pressure causes the sealant to be pressed against the shaft and therefore promote its adhesiveness with respect to the shaft, along the gaps between finely spaced surface-texture irregularities. As a sufficient amount of sealant adheres to the portion of the shaft which is exposed to the sealant, the clearance between the shaft and the housing is reduced. The pressure differential between the working volume and the stuffing box is sufficiently reduced, or completely eliminated, to prevent working fluid leakage. Frictional forces acting on the shaft as it is rotated about the wall of the shaft opening result in erosion and diminishment of the sealant, and eventually the surface tension of the remaining sealant is not sufficient to prevent the leakage of the working fluid from a shaft opening.
Heretofore, the stuffing box has not been provided with means for indicating the occurrence of, or the rate of, sealant diminishment. Maintenance workers therefore replenish the sealant by use of the injection device upon estimation of sealant diminishment, when in reality there may be no need of a maintenance operation, or after an indication of working fluid leakage from the shaft opening. To reduce the number of time consuming and cost incurring maintenance operations, some maintenance workers tend to pressurize the sealant to a pressure greater than a suggested limit. When the injected sealant is overly pressurized, the solidified sealant overheats due to the increased frictional forces acting thereon. Heat is therefore transferred from the overheated solidified sealant to the working fluid. If the working fluid is water, for example, its temperature can exceed the maximum allowable working temperature and therefore is liable to boil or cavitate. There is therefore a need for an apparatus that can deliver sealant to a stuffing box on demand.
EP 0589138 discloses a spring loaded injectable packing fitting. A packing chamber between a valve stem and valve bonnet has a spring loaded packing injector, which replenishes the packing material normally lost during operation of the valve. The packing is injected through a check valve prior to use. This spring loaded fitting is suitable for the low speed of a valve shaft, but not for the high speed of a rotary machine shaft. Also, the spring induced load to which the fitting is exposed varies throughout the displacement of the spring. Thus the injector delivers the packing at a variable non-optimal pressure, which, when used for a high-viscosity non-Newtonian sealant, may be less than a minimal stuffing box sealant pressure suitable for preventing the leakage of the working fluid from a shaft opening or may be greater than a suggested limit.
It is an object of the present invention to provide an apparatus for delivering a viscous sealant to a stuffing box on demand.
It is an additional object of the present invention to provide an apparatus for delivering a viscous sealant at a predetermined pressure to a stuffing box.
It is an additional object of the present invention to provide an apparatus for delivering sealant to a stuffing box that requires a considerably reduced intervention of maintenance workers with respect to apparatus of the prior art.
It is an additional object of the present invention to provide an apparatus for delivering sealant to a stuffing box at an optimal replenishing time.
It is yet an additional object of the present invention to provide a sealant delivering apparatus of low cost.
It is yet an additional object of the present invention to provide an apparatus which reduces or prevents sealant overheating.
It is yet an additional object of the present invention to provide an apparatus which facilitates reduced sealant pressure while maintaining an equivalent level of sealing and of overall machine efficacy.
Other objects and advantages of the invention will become apparent as the description proceeds.